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Centro de Radioastronomía y Astrofísica, UNAM

Centro de Radioastronomía y Astrofísica, UNAM. Centro de Radioastronomía y Astrofísica, UNAM. Massive Star Formation. Luis F. Rodriguez, CRyA, UNAM Morelia, México. Introduction The paradigm for low-mass star formation The search for jets and disks in massive young stars

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Centro de Radioastronomía y Astrofísica, UNAM

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  1. Centro de Radioastronomía y Astrofísica, UNAM

  2. Centro de Radioastronomía y Astrofísica, UNAM

  3. Massive Star Formation Luis F. Rodriguez, CRyA, UNAM Morelia, México • Introduction • The paradigm for low-mass star formation • The search for jets and disks in massive young stars • Other mechanisms? • Conclusions

  4. HH 1 HH 2

  5. HH 1-2 VLA 1 VLA 1

  6. LOW MASS STAR FORMATION • Fragmentation of cloud • Gravitational contraction • Accretion and ejection • Formation of disk • Residual disk • Formation of planets (Shu, Adams & Lizano 1987)

  7. L1551 IRS5: Binary system with disks. VLA 7mm Lim & Takakuwa (2006) Minus third component and jet contribution

  8. L1551 IRS5: Binary system with jets VLA 3.6 cm Rodriguez et al. (2003)

  9. Evidence for circumbinary disk also from Takakuwa et al. (2004)

  10. Formation of Massive Stars • With great advances achieved in our understanding of low mass star formation, it is tempting to think of high mass star formation simply as an extension of low mass star formation. • That is, assume that the accretion into the star continues until we have a massive object. • However…

  11. One observational approach has been the search for disks and jets in massive forming stars. • I will talk mostly of a handful of sources that we have studied with collaborators from many institutions.

  12. What are the thermal jets? • (Partially) ionized, collimated outflows that emanate from young stars. • Detectable as weak free-free sources. • They are believed to be the “base” of the large scale outflow phenomena like the bipolar outflows and HH systems. • They are almost always found in the case of low-mass protostars, but rarely in high-mass protostars.

  13. HH 80-81 (GGD27) in L291 dark cloud Distance 1.7 kpc (Rodríguez et al. 1980), Luminosity: 2 x 104 LSol Star: B0.5 ZAMS

  14. Highly collimated jet with extension of 5.3 pc (11´ ) (Martí, Rodríguez & Reipurth 1993)

  15. H2O maser Thermal Jet Gómez et al. 1995

  16. Marti et al. (1998) analyzed the thermal jet over several years.

  17. Derive velocities for knots of 500 km/s.

  18. One of the best cases is Cep A HW2 (Patel et al. 2005) Dust (colors) and molecular (CH3CN, in green contours) emissions perpendicular to bipolar jet. Radius of disk = 330 AU Mass of disk = 1-8 MSUN Mass of star = 15 MSUN SMA and VLA data

  19. Sequence of images of radio jet at 3.6 cm Curiel et al. (2006)

  20. The controversy… • Brogan et al. (2007) and Comito et al. (2007) argue that not a disk but multiple condensations: Outflowing 3.6 cm knots and 875 microns SMA image also shown.

  21. Torrelles et al. (2007) argue for a continuous structure that can be imaged with various tracers.

  22. IRAS 16457-4742 At a distance of 2.9 kpc, it has a bolometric luminosity of 62,000 solar luminosities, equivalent to an O8 ZAMS star.

  23. Garay et al. (2003) found millimeter continuum emission (dust) and a triple source in the centimeter range. Core has 1,000 solar masses. Data from SEST (mm) and ATCA (cm)

  24. Australia Telescope Compact Array

  25. Data from ATCA, the components are not clearly resolved.

  26. VLA images of IRAS 16547-4247

  27. The outflow carries about 100 solar masses of gas (most from ambient cloud) and has characteristics of being driven by a very luminous object.

  28. Molecular hydrogen (2.12 micronss) tracing the bipolar outflow (Brooks et al. 2003) Data from ISAAC in the VLT

  29. OK, so we believe we have a jet • What about infalling gas and in particular, a disk?

  30. Some of the line emission from single dish (20”) observations show profiles characteristic of large scale infall. You need much larger angular resolution to detect a disk.

  31. The SubMillimeter Array

  32. Velocity gradient in SO2 (colors) suggests total mass of 20 to 40 solar masses and a radius of 1,000 AU for the disk (Franco-Hernandez et al. 2007). Most massive young star known with jets, disk, and large scale infall.

  33. Also water masers suggest rotating structure with same direction as SO2, but at much smaller scales. Keplerian mass also about 30 Msun

  34. Do we need merging? • Evidence for collimated outflows from massive young stars is relatively firm. Collimated outflows not expected after merging. • Evidence for disks is scarce, but is being searched for vigorously. Some good cases. • There is, however, the intriguing case of Orion BN/KL.

  35. Three stellar sources seem to be receding from the same point (Gomez et al. 2005, 2007), at velocities of 10-20 km/s.

  36. Indeed, around the BN/KL region there is the well known outflow with an age of about 1000 years. It is possible that the outflow and the ejection of BN and I were result of the same phenomenon. Energy in outflow is of order 4X1047 ergs, perhaps produced by release of energy from the formation of close binary or merger.

  37. Still many open questions in massive star formation... • Are disks and jets always present? • Accretion seems needed given presence of outflow phenomena. • Are mergers playing a role?

  38. Thank you

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